Continuously adjustable gear system

ABSTRACT

The invention relates to a gear system. The further development of said gear system is characterized in that the geometry of the coupling elements ( 13 ), the peripheral groove and the positive locking elements ( 12 ) of the annular disk ( 10 ), together with that of the guides of the star-shaped disk and the distance between the annular disk ( 10 ) to the star-shaped disk is selected in such a way that the forces occurring when the charge arc as it passes between the coupling element ( 13 ) and the star-shaped disk result in the production of a positive-locking contact or reinforce said contact, whereby the pressing force produces a moment which holds the coupling element ( 13 ) in a plane-parallel position with respect to the annular disk ( 10 ) and the star-shaped disk, said moment being greater than the tilting moment which is determined by the distance between the active plane on which force is transmitted from the annular disk ( 10 ) to the coupling elements ( 13 ) and the active plane on which force is transmitted from the coupling elements ( 13 ) to the star-shaped disk.

The invention relates to a stepless transmission with a ring having aforce-transmitting formation, preferably with teeth, and a peripheralgroove, and concentrically or eccentrically positionable relativethereto a center wheel with radial guides, and with at least twocoupling elements that each ride at one end in the peripheral groove andthat have force-transmitting formations complementary to theforce-transmitting formation and that each at the other end have aforce-transmitting pin projecting axially into and shiftable in arespective one of the radial guides of the center wheel, each couplingelement moving on orbiting in the peripheral groove of the gear througha force-transmitting zone in which the coupling element is engaged withthe force-transmitting formations of the gear and that otherwise is in afree-running zone in which it is disconnected (decoupled) and where byvarying the eccentricity of the center wheel and ring the transmissionratio is changeable.

Such a transmission is for example described in German 199 53 643.

According to EP 0,708,896 a stepless or nearly stepless transmission isknown having a driving and a drive member and several individual gearsthat together form a satellite assembly that is in constantforce-transmitting connection with a central gear. If the relationshipof the effective radius of the satellite assembly and the central wheeland the eccentric position of the satellite assembly and the centralgear are varied relative to each other by appropriate means, thetransmission ratio between the driving and the driven member iscorrespondingly varied. The gears forming the satellite assembly orbitcyclically when the central gear is eccentric through aforce-transmitting zone and a free-running zone, the gears beingarranged to orbit about the satellite-assembly axis and to rotate viarespective unidirectional clutches about their own axes. On moving fromthe free-running zone to the force-transmitting zone the gears enterinto force-transmitting engagement by blocking fo their rotation fortorque transmission. There is some variation in the transmission oftorqued caused by the variation in the radius as the force-transmittingzone is traversed and/or the effective tangential component is partlycompensated by cyclical control. In one concrete embodiment that isdescribed in this publication, the coupling elements are carried on therim of the driving member and can move along radial grooves in thedriven member. The coupling elements are interconnected by differentdirection sensitive force and/or shape effects so that at any time thatcoupling element is effective to transmit torque that leads to thehighest angular speed in the driven member.

In EP 1,003,984 there is another such transmission with satellite orwedge elements that is comprised of a one- or multi-part base and a one-or multi-part contact body that in a force-transmitting position locksin the guide of the drive member, projecting wedge-body pins or anelement connected to the wedge body having two parts, normally axiallyoffset, fitted in radial guides of the driven member. The wedge elementscan according to another embodiment be formed by contact bodies ofnonround section, one surface portion of the contact body having aradius of curvature generally the same as the radius of curvature of theannular groove wall of the ring with which this surface portion forms afriction connection in the force-transmitting position, so that Hertzpressure is minimized, the relationship of the radii being between 0.6and 1.4.

It is critical for the operation of these transmission that theoperation of the satellite or coupling elements be compact, fast, andaccurate. The goal of fast-acting coupling and decoupling action isanalogous to that of free-running clutches, but they are different fromthe transmission discussed here. Free-running clutches always have quitea few coupling elements that can engage and disengage at any position,with wedge-body transmissions (so-called satellite transmissions) thecoupling and uncoupling always take place at specific locations, that iswhen the force-transmitting zone is entered, so that at any time onlyone coupling element is engaged and the remaining coupling elements aremoving through their free-running zones. With satellite transmissions itis also highly important that the coupling elements which each must allalone transmit force from the ring serving as drive body to the centerwheel serving as driven body, while with free-running clutches the forcetransmission takes place between inner and outer rings between which thewedge bodies rotate and normally via all the wedge bodies. Intransmission the number of couplings and the force transmission via asingle coupling element is normally also higher.

It is thus an object of the present invention so to improve thedescribed stepless transmission that the transmission is simple and surein operation.

This object is achieved by the transmission according to claim 1.

The steplessly variable transmission according to the invention has aring with a peripheral groove and force-transmitting formations thatpreferably are formed as an annular row of teeth. This peripheral grooveserves as a guide for coupling elements having force-transmittingformations, e.g. teeth, complementary to the force-transmittingformation of the ring and serving for transmitting force to the teeth ofthe ring. These coupling elements orbit through a torque-transmittingload zone that extends over an arc, and a free-running zone. On enteringthe load zone the wedge elements are coupled, that is theforce-transmitting elements of the ring and the complementaryforce-transmitting elements of the wedge body engage one another inforce-transmitting contact since the coupling elements pivot about theirintegral axes that preferably extend parallel to the pivot axis of thering and of the center wheel. This force-transmitting contact ismaintained through the entire load zone. When moving from the load zoneto the free-running zone the wedge bodies are pivoted back to disconnectthe force-transmitting formations. Each coupling element has an axiallyprojecting force-transmitting pin shiftable in a respective one of theradial guides of the center wheel and transferring force during movementalong the load zone to the center wheel. This so-called one-sided forcetransmission has the advantage that it simplifies the construction ofthe transmission.

The eccentricity of the center wheel and ring changes transmissionratio. The force-transmitting pins move as the transmission ratio ischanged in the radial guides, that can be grooves or radially extendingsurfaces of pivotal wedge jaws that are pivotal toward one another oncethe transmission ratio is set to fix the desired position of theforce-transmitting pins. The radial guides can be straight or slightlycurved.

According to the invention the geometry of the coupling elements, thegroove and the force-transmitting formation of the gear as well as thecenter wheel with its guides and the spacing of the gear to the centerwheel are selected such that on moving through the force-transmittingzone the forces between the coupling element and the center wheel forceor urge the parts together with a coupling force creating a torqueholding the coupling element parallel to the gear and the center wheeland greater than the canting torque that is produced by the spacingbetween the effective plane of force transmission from the gear to thecoupling elements on one side and the effective plane of the forcetransmission from the coupling elements to the center wheel on the otherside. Preferably the force-transmitting formations of the ring and ofthe coupling element have the maximum number of teeth along their edgesin order to increase the shifting precision that is determined by thetooth pitch. With a given circumference of the ring, the teeth aresmaller when more of them are used. Small teeth have of course onlysmall contact surfaces. Since the surface pressure of the teeth islimited by what the material can bear, under some circumstances theamount of torque that can be transmitted is very limited. For thisreason each coupling element has unlike the standard pawls infree-running clutches a contact face with force-transmitting formationsconstituted by a number of teeth, which teeth mesh with theforce-transmitting teeth of the ring. To increase the amount oftransmissible angular force the wedge elements are constructed such thatangular forces transmitted through the couplings element produce arotation moment M1 that is always bigger than the rotation moment M2produced by tooth-flank forces and tending to demesh them. In additionthe transmissible torque is increased in that the friction at theforcibly pressed together contact faces works along with the componentsof the tooth forces in the angular direction.

With the selected one-sided force transmission from the couplingelements to the center wheel the effective lines of the incoming andoutgoing forces lie in respective planes spaced apart by le. As a resultof the existing equilibrium the incoming force F_(ein) and outgoingforce F_(aus) are the same and opposite, that is they satisfy theequation F_(ein)=F_(aus). The coupling element is subjected to thecanting moment M_(kipp)=le×F_(aus), inhibiting rotation of the couplingelement out of a position parallel to the plane of the ring and centerwheel. The geometry of the wedge body is selected such that the rotationmoment M1=F_(ein)×le initiates a pressing force in the teeth that leadsto a stabilizing moment M_(S) that is larger than the canting momentM_(kipp).

The described solution can be put into practice for all practical andimaginable load conditions of the transmission since with the selectedgeometry of the transmission all the forces that lead to theabove-defined moments are proportional to the applied torque. Theselectable geometric parameters are in particular the tooth angle of theteeth, the height of the teeth, the mechanically effective width of theteeth, the mechanically effective length of the force-transmitting pin,the radius of curvature of the ring, the diameter or the length of theslide edge of the wedge element on the ring, the spacing between thering and the center disk, the effective wedge angle of the wedgeelement, and the coefficient of friction of the teeth. The stabilitythat is the goal of the transmission can also be ensured when the designof the transmission not only takes into account the forces applied tothe ring and center wheel, but also the forces effective perpendicularthereto that have torques or lever effects as a result of the relativeorientations of the wedge elements.

Preferred embodiments of the invention are described in the dependentclaims.

Thus preferably the effective width of the force-transmitting formationswhen decoupled is at least as big as the sum of the mechanicallyeffective length of the force-transmitting pin and the spacing, that isthe gap, between the ring and the center wheel. This essentialrequirement is based on the fact that the force distribution on thevarious surfaces under actual conditions is generally axially and theparts have no significant elasticity, so that the stabilizing influenceof friction on the surfaces of the teeth, which extend parallel to theplane of the rim surfaces of the ring, is not taken into account.

Preferably contact surfaces in the ring that serve to guide the couplingelements and exert the frictional forces, are so shaped and orientedthat the effective line of the resultant of all frictional forces isthen further (or nearer) from the center of the ring than the effectiveline of the resulting force between the coupling element and the centerwheel when the effective line of the tooth forces is also further (orcloser) from the center of the ring than the effective line between thecoupling element and the center wheel. Even this feature serves to avoidcanting of the wedge element in directions other than the pivotdirection for coupling and decoupling.

In a further embodiment the coupling elements are not or not only guidedin an annular groove but instead or also are braced directly radially bythe force-transmitting pin on the run-on disk or a roller is fitted tothe force-transmitting pin that itself rides on the run-on disk. Inaddition in a particular variant there is a run-on disk on the ring thatlies below the force-transmitting disk. In this case theforce-transmitting disk extends from the coupling element to the centerwheel through the annular slot that the two run-on disks form. In thiscase the annular groove in the ring is not strictly necessary and can beeliminated. The advantage of this solution is not only in its compactconstruction but also in the limited canting moment when sliding, sincethe guiding forces in contact with the run-on disk(s) are spaced quite abit from the guide forces in the center wheel and thus the length of theeffective lever arm is reduced.

According to a further embodiment of the invention the coupling elementseach have an axial bore that is above and parallel to the pivot axis ofthe respective coupling element and parallel to and above the pin axisand that holds a compression spring that bears at one side on a run-ondisk so that the coupling element is axially guided and so that all orat least most of the frictional forces engage outward of theforce-transmitting pin so that on direction change the applied angularforces produce a moment helping the coupling or decoupling torque. Thisspring thus serves to elastically bias the wedge element against lateralcanting when it is sliding.

According to a further embodiment of the invention the ring has anotherring surface parallel to a surface of the force-transmitting formation,a spring having one end bearing on it and another free end bearingelastically on the coupling element, an angle (α) between the connectingline of the contact point on the surface and the contact point of thespring on the coupling element and the radial line through the contactpoint of the spring on the coupling element complying with the formulatan(α)≦μ, where μ is the coefficient of friction between the spring (19)and the surface (18).

In order to solidly lock the coupling elements when transitioning fromthe free-running zone to the force-transmitting zone, the torqueeffective on the coupling elements must be greater than the torqueresulting from the product of the friction and the spacing a, thisspacing a being the distance to the first force-transmitting elementcoming into engagement with the force-transmitting formation of the ringfrom the wedge-element axis.

To further optimize the functioning of the coupling elements the centerof all masses that rotate on coupling of the coupling element liegenerally on the pivot axis about which the coupling element rotateswhen coupling (or decoupling).

According to a further embodiment of the invention theforce-transmitting formation is formed with angled teeth. The fit of thecoupling elements in the peripheral groove of the ring and of theforce-transmitting pin in the radial guides of the center wheel is astight as possible in order to ensure the parallel positioning of thecoupling elements and also to prevent canting with wedging andself-locking.

In order to provide optimal setting accuracy, the force-transmitting pinhas a ring that is eccentric to the force-transmitting pin. Thetorque-producing angular force is applied by the ring to the couplingelement, with which the ring or the rings in the radial grooves of thecenter wheel are entrained angularly so that the rings roll instead ofslide. The same is true for sleeves mounted on the ends of theforce-transmitting pins that roll in the radial grooves of the centerwheel or on the annular groove of the ring. The angular force on thecontact location between the radial groove of the center wheel and thissleeve brings to be due to the eccentric offset between theforce-transmitting point on one side and the ring with the sleeve on theother side a rotation moment that turns the coupling element accordingto the direction of the force into or out of mesh. Since the eccentricoffset can be set if desired very small and the spacing of the toothupper surface from the coupling element can correspondingly be muchlarger, a lever-arm relationship is possible that with small relativemovements of the contact points in the radial groove causes biggermovements in the teeth of the coupling element. The useless dead travelthat impairs the desired or required accuracy, is thus quite small; theshifting accuracy can be set to the tooth pitch. In fact afterengagement or coupling of the coupling element there is no more slide orroller movement in the teeth, that is all the teeth are active and carryload. The dimensioning of the tooth-foot load depends thus not on thesize of the individual teeth, but only on the width of the couplingelements.

Further embodiments of the invention are described with reference to thedrawing. Therein:

FIG. 1 is an exploded view of the ring with the peripheral groove and agear, a wedge element, and a run-on disk;

FIG. 2 shows these parts in a transparent view without the axialexplosion offset;

FIG. 3 is a side transparent view of the ring and a coupling element inforce-transmitting position;

FIG. 4 is a perspective transparent view of the arrangement of FIGS. 2or 3 with an additional spring-biasing of is the coupling element;

FIG. 5 is a side view of the structure of FIG. 4;

FIG. 6 is a perspective view like FIGS. 2 and 3 with an additional guidefor the planar orientation of the coupling element;

FIG. 7 is a side view of the structure of FIG. 6;

FIG. 8 is a transparent view of a coupling element with aforce-transmitting pin and also showing the forces and torques effectiveduring coupling; and

FIG. 9 is a schematic side view of a coupling element and a part of aring also showing frictional forces;

FIG. 10 is a perspective view of a wedge element and a part of the ringwith a roller 22 on the force-transmitting pin that engages the run-ondisk.

Basically the transmission corresponds to that shown in EP 0,708,896, EP1,003,984, and DE 199 53 643.

The satellite transmission has a ring 10 with a peripheral groove 11 inwhich coupling elements 14 formed as wedge bodies ride. These couplingelements move in a circular path in the groove through an arcuatetorque-transmitting zone and an arcuate free-running zone, pivoting ofthe coupling elements creating contact with the groove that as is knownin the art either results in sliding or as shown in FIG. 1 in forcetransmission, so that the applied torque is transmitted to the centerwheel. To this end the coupling elements each have an axially projectingforce-transmitting pin 14 that, as also known in the art, engages in arespective radially extending guide groove of the center wheel. Insteadof these radial guides in an unillustrated center wheel pivotal wedgejaws can be provided on the center wheel that swing apart to grip theforce-transmitting pins and thus fix them radially on the center wheel.The position—concentric or eccentric—of the center wheel with respect tothe ring determines the transmission ratio. The ring and the centerwheel are parallel to each other.

FIG. 1 shows in exploded view with axial offset a segment of the ring 10with the groove 11 as well as force-transmitting formations 12, which inthis case are formed as a ring gear. A face of the wedge element 13turned toward the gear 12 has complementary teeth. Preferably there areseveral parallel rows of teeth that have an axial dimension that in thiscase is greater than that of the force-transmitting formations of thecoupling element. The arrangement in FIG. 1 is one sided, since force istransmitted to the center wheel only on one side, that is via theforce-transmitting pin 14. The coupling element 13 has an axial bore 15that holds a spring 16 that bears in one direction on the ring and inthe other end on the run-on disk 17 so that the coupling element 13 isaxially guided and at the same time all or at least most of thefrictional forces are effective above the force-transmitting pins 14 sothat on direction change the applied angular force produces a couplingmoment on entering the torque-transmitting zone and a decoupling momenton leaving the torque-transmitting zone. The arrangement of these partsin assembled condition is shown in particular in FIG. 2.

FIG. 3 shows in a side view the position of the coupling element 13 whencoupled, where the gear 12 is in force-transmitting engagement with theteeth of the coupling element 13, created by pivoting of the couplingelement 13 on entry into the torque-transmitting zone. When the couplingelement 13 swings back on leaving the torque-transmitting zone andentering the free-running zone, the parts are disconnected from eachother. In the force-transmitting position (from the ring 10 to theunillustrated center wheel) an angular force U is applied to theforce-transmitting pin 14 of the coupling element 13. The geometry ofthe coupling formation in this case is such that at the illustratedangle of 30° there is in the center of the teeth a normal force N bymeans of which the teeth of the coupling element 13 are pushed into theteeth of the ring gear 12 and thus are capable of transmittingconsiderable angular force through small parts without the interengagedgear 12 and the coupling element 13 jumping apart. With steeper teethand a smaller angle than the illustrated one of 30° this normal force iseven greater.

In a further embodiment according to FIG. 4 a peripheral groove 18 isformed centrally in the gear 12 so as to subdivide the gear 12 into twotoothed rings. The coupling element 13 is similarly split at its teeth.A spring 19 engages into this groove 18, here a wire spring with anupper bent-over end and an opposite inner end fixed on the wedge element13. The spring 19 rides in the groove 18 and is guided by it. Thecoupling element 13 and its spring 19 are set such that in thearrangement of FIG. 5 the contact point of the spring 19 on the floor ofthe groove 18 forms with the contact point of the wedge element 13 inthe groove of the ring 10 an angle α that in this arrangement is 6 (theother leg being formed by a radial line). The tangent of this angle(here 6°) is smaller than the relationship of the normal force to thefriction, that is smaller than the coefficient of friction μ. For 6°there is: tangent 6°=0.11<μ. Thus without external control, simplespring action lifts the coupling element 13 in the free-running zonefrom force-transmitting contact (with the teeth) and in thetorque-transmitting zone automatically establishes theforce-transmitting connection.

In order to avoid a situation in which the teeth are only partiallyintermeshed, in a further embodiment the tooth shape, that is the shapeof the force-transmitting formations, is selected such that the sum ofthe moments that are produced by friction during sliding of the teethand that are effective opposite to the movement during coupling byswinging of the coupling element, is always smaller than the moment thatserves for coupling or locking.

FIG. 6 shows an embodiment of the transmission where the parallelposition of the clamping element 13 is established in that it has agroove-shaped slot 21 in which a guide ridge 20 engages that projectscentrally from the gear 12 and that subdivides the gear 12 axially intotwo gear halves. As in FIG. 1, the wedge element 13 can also have a borefor holding a spring 16 that is braced on one end on the guide ridge 20(if necessary left and right).

As shown in FIG. 8, diametrally opposed forces F_(ein) and F^(aus) bearon the coupling element 13, ideally centrally of the coupling formationsand centrally of the force-transmitting pin 14. This force balancing isachieved with the tightest possible tolerances equal to zero along withthe requirement that the coupling element be a rigid body, when meshingof the teeth prevents a canting of the coupling element in spite of thetorque moment M_(kipp).

As shown in FIG. 9 the gear has a radius Rz and the force-transmittingpin 14 orbits with its pivot axis on a radius Run. The axially effectivespring 16 from FIG. 1 slides on a radius R_(gl) on which the friction ofthe plane-parallel guiding of the wedge element 13 engages, resultingfrom the sliding action of the wedge element. Positive latching torqueis produced by satisfying the equation R_(gl)>_(Run).

All of the parts that pass the coupling elements 13 are guided at oneend in the ring 10, in the teeth 12, and in the radial grooves of thecenter wheel. In order to make this linear guiding as loss-free aspossible, the interfit tolerances must be tight enough to ensureparallel positioning of the wedge element or elements, on the other handit is essential to prevent canting that would produce wedging orself-locking. To this end the fit is such that, when passing, thecoupling elements 13 are guided by springs on the ring so that there isno wedging action, but instead all the tipping torque M_(kipp), which iscaused by the one-sided force deflection, is resisted by spring force.The spring characteristic and the spring prestress thus prevent anydeflection allowing contact of any hard parts, in particular the nestedcurved peripheral parts with resultant wedging. In the coupled conditionof the coupling formations on the other hand the stabilizing force ofthe meshing teeth is dominant and holds the wedge body guided in thegroove and its force-transmitting pin parallel in the center wheelwithout canting.

In a further embodiment the teeth can be angled so that the wedgeelement 13 when meshing is pushed into the floor of the groove of thering 10 and is thus stabilized against canting.

In use each coupling element is acted on by a number of forces, as forexample mass forces from intermittent phases in rotation, centrifugalforces, Coriolis forces, and frictional forces at the various contactsurfaces. These forces are effective along different lines and indifferent planes so that the moments together ensure the engagement anddisengagement of the coupling elements during rotation and theirparallel positioning.

When the coupling elements are free running these forces can be usedpositively, because the coupling action should and must be simultaneousat any location along the circumference and by all elements. To this endfor example permanently applied forces can be used in order to hold thepawls or wedge bodies in constant contact in guide pockets or clamprings. In addition it is possible to use springs that ensure suchpermanent contact.

With the above-described satellite transmission on the other hand thedescribed permanently effective forces and torques around the entireperiphery are disturbance factors since at any given time during forcetransmission only one of the coupling elements is actually transmittingforce, while the other coupling elements are decoupled and in theirfree-running mode. For a smooth and friction-free operation with asatellite transmission only those forces and torques are used that pressthe coupling elements in their force-transmitting zones into the teethand that raise them therefrom in their free-running zones. When movingfrom the force-transmitting zone to the free-running zone the forceeffective on the force-transmitting pin reverses, since theforce-transmitting pin on moving along the force-transmitting zonetransmits force and on running through the free-running zone is onlyentrained or shifted by the center wheel. In order to rotate thecoupling elements so as to couple and decouple it, as a result onlythose forces are used that form together with the force on the pin aforce pair that causes coupling on entry into the force-transmittingzone and decoupling on leaving the force-transmitting one or reinforcesthis movement.

To suppress unwanted moments the coupling elements are balanced suchthat the pivot axis of the latching movement is ideally through or atleast near the center of all the masses moving during coupling. Inaddition all contacts that are geometrically or physically necessaryduring the relative movement of the coupling element and the gear forguiding and the associated frictional forces are set such that theyproduce relative to the effective line of the forces on theforce-transmitting pin positive latching moments. This is achieved inpart by selection of the radii according to FIG. 9.

A further advantage is provided by the spring 16 that elasticallysuppresses lateral canting of the coupling elements when sliding, sothat a generally constant (friction) force is produced that duringcoupling and decoupling positively reinforces the pivoting action of thecoupling elements.

The already described spring 19 is effective in the same manner on theannular surface 18.

As shown in FIG. 10, preferably there is a roller 22 on theforce-transmitting pin that rides on the run-on disk 17 so that thecoupling element is guided on the rim of the gear with the leastpossible likelihood of canting.

1. A stepless transmission with a ring (10) having a force-transmittingformation (12), preferably teeth, and a peripheral groove (11), andconcentrically or eccentrically positionable relative thereto a centerwheel with radial guides, and with at least two coupling elements (13)that each ride at one end in the peripheral groove (11) and that haveforce-transmitting formations complementary to the force-transmittingformation (12) and that each at the other end have a force-transmittingpin (14) projecting axially into and shiftable in a respective one ofthe radial guides of the center wheel, each coupling element (13) movingon orbiting in the peripheral groove (11) of the gear (10) through aforce-transmitting zone in which the coupling element (13) is engagedwith the force-transmitting formations (12) of the gear (10) and thatotherwise is in a free-running zone in which it is disconnected(decoupled) and where by varying the eccentricity of the center wheeland ring the transmission ratio is changeable, characterized in that thegeometry of the coupling elements (13), the groove and theforce-transmitting formation (12) of the gear as well as the centerwheel with its guides and the spacing of the gear to the center wheelare selected such that on moving through the force-transmitting zone theforces between the coupling element (13) and the center wheel force orurge the parts together with a coupling force creating a torque holdingthe coupling element (13) parallel to the gear and the center wheel andgreater than the canting torque that is produced by the spacing betweenthe effective plane of force transmission from the gear to the couplingelements on one side and the effective plane of the force transmissionfrom the coupling elements to the center wheel on the other side.
 2. Thetransmission according to claim 1, characterized in that the effectivewidth of the force-transmitting formations when decoupled is at least asbig as the sum of the mechanically effective length of theforce-transmitting pin and the spacing, that is the gap between the ringand the center wheel.
 3. The transmission according to claim 1,characterized in that contact surfaces in the ring (10) that serve toguide the coupling elements (13) and exert the frictional forces, are soshaped and oriented that the effective line of the resultant of allfrictional forces is then further (or nearer) from the center of thering than the effective line of the resulting force between the couplingelement and the center wheel when the effective line of the tooth forcesis also further (or closer) from the center of the ring than theeffective line between the coupling element and the center wheel.
 4. Thetransmission according to claim 1, characterized in that the couplingelements each have an axial bore that is above and parallel to the pivotaxis of the respective coupling element and parallel to and above thepin axis and that holds a compression spring (16) that bears at one sideon a guide wall (17) (run-on disk), that extends parallel to the planeof the ring, and of the center wheel, and that on the other end bears ona nearly parallel guide wall of the peripheral groove (11) or that thereis such a spring in the coupling element between the guide wall and theperipheral groove.
 5. The transmission according to claim 1,characterized in that the ring (10) has another ring surface (18)parallel to a surface of the force-transmitting formation (12), a spring(19) having one end bearing on it and another free end bearingelastically on the coupling element, an angle (α) between the connectingline of the contact point (19) on the surface (18) and the contact pointof the spring on the coupling element and the radial line through thecontact point of the spring on the coupling element complying with theformula tan(α)≦μ, where μ is the coefficient of friction between thespring (19) and the surface (18).
 6. The transmission according to claim1, characterized in that the torque of the coupling elements (13) isgreater when moving from the free-running zone into theforce-transmitting zone than torque (Mr) resulting from the product ofthe friction (R) and the spacing (a) between the firstforce-transmitting element coming into engagement with theforce-transmitting formation (12) of the ring from the wedge-elementaxis.
 7. The transmission according to claim 1, characterized in thatthe run-on disk (17) bears directly or via a roller (22) with theforce-transmitting pin (11) so that the coupling element is guided bythis contact on the rim of the ring with the least possible cantingeffect.
 8. The transmission according to claim 7, characterized in thata second run-on disk is set on the inner radius and forms with the firstrun-on disk (17) an annular slot through which the force-transmittingpin (14) projects out of the coupling element and thus or via a roller(29) indirectly serves for guiding the pin (14) on the periphery withthe smallest possible canting action.
 9. The transmission according toclaim 1, characterized in that the center of all masses that rotate oncoupling of the coupling element (13) lie generally on the pivot axisabout which the coupling element rotates when coupling.
 10. Thetransmission according to claim 1, characterized in that theforce-transmitting formation (12) is formed with angled teeth.
 11. Thetransmission according to claim 1, characterized in that the fit of thecoupling elements (13) in the peripheral groove (11) of the ring (10)and of the force-transmitting pin (14) in the radial guides of thecenter wheel is as tight as possible.
 12. The transmission according toclaim 1, characterized in that the coupling element has a groove in theforce-transmitting formations and in which a disk-shaped guide of thering can slide.
 13. The transmission according to claim 1, characterizedin that a ring is employed with a preferably round shape eccentric tothe force-transmitting pin (14) so that the force that is exerted by thering (10) on this ring produces rotation of the coupling element (13)about the longitudinal axis of the pin (15).
 14. The transmissionaccording to claim 13, characterized in that sleeves are mounted on therings and/or over the end of the force-transmitting pins (14) that rollinstead of slide in the radial grooves of the center wheel and/or in theperipheral groove (11) roll.
 15. The transmission according to claim 13,characterized in that the ring and/or the sleeve and/or theforce-transmitting pin (14) have a collar that when loaded holds theforce-transmitting pin (14) and the coupling element parallel to thering (10).
 16. The transmission according to claim 1, characterized inthat by a guide element, preferably a guide pin, ana air or liquid guideor a magnet for externally controlling the movements of the couplingelements.